Fabricpath spine learns tons of MAC, why?

This may be off topic. Just see anybody can shed some light on it.

We have 2 Nexus 7706 (running V6.2.8) at the core. The devices are the
spine of our fabricpath topology. A bunch of other Nexus 7706 leaves
connect to the core using fabricpath mode. Theoretically, the spine should
not see individual MAC addresses. Unfortunately, the spine sees almost the
same number of MACs as seen on the fabricpath leaves. The
destinations/paths are correct. They use switch IDs, not CE or trunk ports.
It seems for some unknown reason, the spine strips off the fabricpath
header and look into the Ethernet header. I double check the ports of the
spine: one management port in routed mode, all connected up/up ports are in
fabricmode, and some notConnected ports are in trunk mode (does this
matter?). Did I miss anything here?

PS: Did anybody successfully bring a 100G link (N77-F312CK-26) up between
two Nexus 7706 boxes running v6.2.8a? We have to downgrade to v6.2.8 to get
the speed.

Thanks,

--
Yuansen Chen
CCIE #20383
Blogs and organic groups at http://www.ccie.net